1. Field of the Invention
The invention relates to epoxy resins having an extremely low content of chlorine, particularly a low content of organically bound chlorine.
2. Description of the Related Art
Epoxy resins have a broad range of applications within electronics and electrical engineering. They are used for molding compounds, glob top materials, printed circuit board materials, adhesives, underfillers, and films and for shielding electronic and optoelectronic components. Bisphenol A diglycidyl ether and bisphenol F diglycidyl ether frequently serve as base materials. As a rule, these are produced by causing the respective bisphenols to react with epichlorohydrin. The ionically bound chloride produced during synthesis can be removed to a low ppm by means of aqueous washing processes. In contrast, organic compounds containing chlorine which develop as byproducts and which cause the epoxy compounds to have a total chlorine content of up to 0.5 percent by weight are not removed by means of aqueous processing. Epoxy resins such as bisphenol A diglycidyl ether or bisphenol F diglycidyl ether with a total chlorine content of less than 100 ppm are hitherto unknown.
U.S. Pat. No. 3,413,320 discloses the purification of epoxy resins using recrystallization to total chlorine contents of approximately 0.37%. Nevertheless, as expected, this slight reduction in the chlorine content does not show any impact on the corrosive behavior of the epoxy resin.
The general assumption is thus that in air, in particular in the presence of heat and humidity, the organically bound chlorine is at least partially converted to chloride ions. Said ions can cause corrosion with parts coming into contact with them.
As a result it is necessary to make available epoxy resins with a low residual chlorine content, in particular of organically bound chlorine, which therefore have less of a tendency to cause corrosion.